The use voltages of modern electronic components tend to be decreasing. For example, new data transfer systems such as those compatible with USB (universal serial bus) version 3.0 require a maximum use voltage of 2V. At the same time, higher operating frequencies are being used by modern electronic components. A suitable ESD (electrostatic discharge protection) protection device for such a low voltage class of higher operating frequency electronic components must have a relatively low trigger voltage e.g. of about 3.5V. That is, the ESD protection device must clamp the use voltage of the electronic component at a relatively low level such as about 3.5V to protect the electronic component from overvoltage conditions.
ESD protection is conventionally provided for electronic components in a low voltage class such as USB version 3.0 compliant devices by connecting a TVS (transient voltage suppression) diode in serial with a low capacitance p-i-n diode. A p-i-n diode is a diode with a wide, intrinsic semiconductor zone between a p-type semiconductor zone and an n-type semiconductor zone. The p-type and n-type regions are typically heavily doped for use as ohmic contacts. A large TVS diode in serial with a p-i-n diode absorbs the energy of an ESD event. TVS diodes are solid state pn junction devices designed to protect sensitive semiconductors from the damaging effects of transient voltages. The surge power and surge current capability of a TVS diode are proportional to the junction area of the diode. Under normal operating conditions, a TVS diode presents high impedance to the protected circuit. Ideally, the TVS diode appears as an open circuit, although leakage current is present. When the normal operating voltage of the protected circuit is exceeded e.g. due to an ESD event, the TVS diode junction avalanches under a breakdown condition and provides a low impedance path for the transient current. As a result, the transient current is diverted away from the protected components and shunted through the TVS diode.
TVS diodes are typically fabricated using inexpensive silicon. Silicon TVS diodes are unidirectional and have a lowest reasonable breakdown voltage of about 5V. The doping levels required to realize a breakdown voltage below 5V are very high, resulting in band-to-band tunneling to occur which causes high leakage currents in the range of several μA at even 2V. Such a breakdown response for a TVS diode is not acceptable for many applications such as mobile systems supplied by batteries. Thyristors can also be used for ESD protection. However, thyristors require a long reverse recovery time of more than 1 μs after an ESD event strike before the thyristor-based protection system can function again.